I wanted to say, I really like the system and the concept, but I think some things could be improved :
- The hunt for Kuva larvlings is a competition inside of a coop game, it's a rush to who will kill it first to get the Lich and I think this could use a redesign. I'm not sure what approach you would like for this but I would spawn as many larvlings as the amount of players who do not currently have a Lich in the mission and allow them to only execute one larvling.
- Nobody likes bonus impact damage on their weapon given the current state of impact damage and its associated status effect.
- I think more coop surrounding the Lich fight and figuring Requiem mods would be nice. I would love a system where players could each equip different Requiem mods in an attempt to identify a Lich's weaknesses. For example, the Lich could be open to a different kind of Mercy from other players that would not remove a health bar but give hints if the player has correct Requiem Mods equipped. Doing so would make the Lich down a player into a bleedout state but it would not make the Lich despawn. Each of these "Mercy from different players" could provide Requiem Murmur and would play different sounds based on the number of correct mods and correct positions. The players would have to learn how to identify the audio cues like "Oh, this sound means that this player had 2 correct Requiem mods and 1 in the right order".
- Tied to my previous point, I would prefer if the Requiem sequence was more of a puzzle, something that could be figured out based on some clues rather than pure random trial and error. For example, in missions controlled by a Lich, there could be hints that you could hunt and scan (like Cephalon fragments). These hints could be puzzles associated with Requiem mods' descriptions. This would make the whole process feel less random and it would reward players for exploring more instead of rushing missions blindly while still not penalizing people who just want to rush.
- I wish the Lich missions and larvling spawning were not excluded from things like fissures, Kuva missions and all. I don't like when multiple things have to be farmed separately like that and it would really feel like the Lich is your Nemesis, that's it's really doing its best to be your pain and that you don't just hop in a mission to voluntarily be taxed. I wish it would be a bit more like a Stalker I guess where it could spawn almost anywhere at any time, summon thralls and other Grineer units to help them.
- I'm not sure about Kuva weapons having a different disposition compared to their normal variants.
I think that's all I have to say. Other than this criticism, I really like the system and I think you did a great job with it overall.